Biogeography: The Geographic Distribution Of Species

Darwin thought up his Theory Of
Common Descent because he had found biogeographic evidence. He
thought that that evidence was much stronger than the fossil
evidence. Scientists still think so.

Basically, some species have suspicious resemblances to supposedly
different species that just happen to live nearby. Often, it would be
better design for them to instead resemble some further-away
species. And, this is the norm. There are a huge number of good
examples.

The trees on the remote island of St. Helena are unlike the trees
anywhere else on earth. Sunflowers are the closest relative to the
strange gumwood tree and to the various cabbage-trees. And, the most
closely related sunflower is the local sunflower. The scientific
explanation is that this volcanic island was originally formed far
away from any continent, and therefore started out with no land
plants. Eventually, some sunflower seeds managed to get there. Since
no one else was filling the role of "tree", the largest
plants on the island - some of the sunflowers - took the
job. Transformed by time and competition and by the demands of their
role, they now look like trees.

Every other remote island has its own examples. In the Galapagos,
the role of woodpecker is taken by a finch. Or rather, it's mostly a
finch, but it has a beak specialized for the woodpecker
role. Apparently, the only land bird which got to the Galapagos was a
finch, so all the land birds there are modified finches. (DNA studies
prove the relationship.)

In Hawaii, the role of woodpecker was taken by a modified
honeycreeper bird. Again, every land bird in Hawaii is a modified
honeycreeper. There's a honeycreeper "parrot" too.

Most remote islands had flightless birds, such as the Dodo. There
is an obvious evolutionary explanation for why these existed on
islands, but not on continents. Birds could get to islands, and ground
animals couldn't. So, the role of ground animal was available, and on
each island, some bird took on the role. From this explanation, we can
predict that each island would have its own unique species of
flightless bird. And that is a correct prediction.

Because of Australia, South America, and the various remote
islands, it's easy to come up with a really long list. For example,
South American tropical species are more closely related to South
American desert species than they are to African tropical species.
Australia's marsupials took on the roles of predator (Tasmanian Wolf),
mouse, mole, wolverine (Tasmanian Devil), and anteater.

The point is that over and over again, evolution explains this very
well. The process of species arrival has been observed on islands
such as Krakatoa, which was wiped clean by a volcanic eruption in
1883. We know that the more remote islands receive very few species
from the outside world. So, the lucky arrivees have a golden
opportunity to take up many new lifestyles, and adapt into them. This
is referred to as an evolutionary radiation into ecological
niches, and it explains (for example) the 700 species of Hawaiian
fruit fly.

Bird are the same on both sides of the Grand Canyon, but there are
different rodents on each side. The obvious explanation is that the
canyon isolates groups of rodents, but doesn't isolate birds.

Fossil biogeography reinforces this point. For example, the
Atlantic Ocean was formed when a supercontinent broke up. Fossils that
date to just before this breakup are the same in Europe as they are in
North America. Fossils from after the breakup show progressively more
and more differences between the land animals (and plants) of the two
continents. The breakup made no difference to ocean creatures.

In short, species are mutable. And, they are not designed according
to any master plan. The faux woodpeckers found on remote islands
aren't as good at it as real woodpeckers. And, real woodpeckers are
found in some treeless places. A good designer would have re-used his
best designs, but instead we find nature has made do with whatever was
at hand.